1. Technical Field
The present invention relates generally to transmitting data over emulated local area networks (ELANs) using internet protocol (IP), where the ELANs are implemented on an asynchronous transfer mode (ATM) network. More specifically, the present invention relates to creating redundant default gateways for the ELANs.
2. Description of the Related Art
Due to the widespread acceptance of the current IP standard for communicating data, this standard has been adapted for use with ATM devices. Currently, one standard solution for sending IP traffic over an ATM interface is specified by the Internet Engineering Task Force (IETF) and is described by M. Laubach in a document entitled "Classical IP and ARP over ATM," RFC 1577, Hewlett Packard Laboratories, January 1994. Also, due to the large installed base of traditional local area network (LAN) products, standards have been created which allow existing LAN applications to communicate data over ATM networks. See ATM Forum "LAN Emulation over ATM: Version 1.0 Specification," AF-LANE-0021.000, January 1995.
A problem existing with today's ELANs which use IP is the lack of flexible backup gateways. In current systems, end stations attached to a router via LAN emulation (LANE) can either run a routing protocol to determine the next hop for packets destined for subnets not directly connected to the end station, or the system administrator can specify the next hop by configuring a default-gateway. The system administrator can configure a default gateway on the end station by specifying the IP address of a router interface on the ELAN. If the system administrator has configured a default gateway and the default gateway's interface is down, the end station will not be able to forward packets out of its own subnet.
Therefore, it would be desirable to have a backup default gateway which would automatically start passing packets to other subnets in the event the primary default gateway failed. The switch from the primary default gateway to the backup default gateway should be transparent to end stations and should occur automatically in the event the primary default gateway fails. Finally, it would be desirable to have the router interfaces associated with both the primary and backup default gateways be active simultaneously. This would allow routing protocols such as OSPF to learn the connectivity of the backup default gateway while the primary default gateway is still active.